Fine pigment tends to demonstrate strong cohesive force between pigment particles in a medium such as an organic solvent or molten resin, and aggregated pigment ends up causing a decrease in tinting strength.
Various pigment dispersing agents and pigment compositions containing such pigment dispersing agents have been proposed for improving pigment dispersibility. For example, an example has been disclosed that combines the use of a pigment having an azo skeleton and a binder resin having an acidic group (Patent Document 1). On the other hand, a toner has been disclosed that contains a block copolymer or graft copolymer, obtained by polymerizing a styrene-based monomer and acrylate-based monomer (or methacrylate-based monomer), carbon black and a binder resin in order to improve the dispersibility of carbon black in the toner (Patent Document 2). Moreover, an azo compound has been disclosed that has a styrene/acrylic-based polymer segment in order to improve the dispersibility of an azo pigment (Patent Document 3).